The present invention relates to a non-contact inspection system for detection and identification of defects in sheets of glass, especially flat automotive glass. The system is intended to operate on a continuous production line at line speed, and for the identification of a wide variety of types of defects, including bubbles, scratches, chips, cracks and edge defects.
In processes for manufacture of glass in sheet form, it is necessary to be able to inspect the sheets of glass for defects. Such defects may be in the form of scratches, bubbles, chips, blemishes and a wide variety of other defects. However, the mere detection of defects is insufficient in that the manufacturer of the sheet glass needs to know whether the defects are insignificant (i.e. minor in nature) and thus acceptable to the customer, or significant (i.e. a major flaw) such that the sheet glass would not conform to specifications established by the customer.
It is possible to use visual inspection of sheets of glass to identify those sheets that have defects. In addition, using visual inspection, it is possible to identify the location and possibly the type of defect. However, visual inspection is not acceptable because of the time and cost involved in conducting a visual inspection, and the limitations of such a method. It would be preferable to be able to conduct the inspection on-line in the production process, at production speeds, so that defects could be rapidly identified and communicated to production personnel and/or the sheets with the defects could be readily and quickly separated from sheets meeting quality specifications in an effective manner.
Methods have been developed for the inspection of sheets of glass using optical techniques. However, such methods have been limited in application, often only capable of identifying a small number of types of defects, and not capable of detecting and identifying the type, magnitude and location of a wide variety of defects. It is therefore an object of the present invention to provide a novel glass inspection system and method.
Apparatus and a method have now been found that are particularly intended for use in inspection of sheets of glass in a production line, at production speeds, in a manner that shows the magnitude, type and location of the defects in the sheet of glass, and especially intended to be an integral part of a glass processing system.
Accordingly, one aspect of the present invention provides an inspection system for a sheet of glass, comprising:
a) a first laser and a second laser, each of the first laser and second laser providing a sheet of light;
b) a cylindrical lens system, said lens system having a focal point on the main optical axis thereof;
c) a first light detection system and a second light detection system;
the first laser being located at the focal point of the lens system, the second laser being located at a distance from the lens system that is greater than that of the first laser, said second laser being located off of the axis of the lens system,
the first light detection system receiving light from the first laser and the second light detection system receiving light from the second laser, and providing information on the variation in intensity of light;
the inspection system being adapted to position and detect a sheet of glass between the lens system and the detection systems.
In preferred embodiments of the apparatus of the present invention, the system additionally comprises a computer executing software that utilizes information from the first and second light detection systems to determine the location, type and magnitude of defects in the sheet of glass.
Preferably, the computer records the location, type and magnitude of defects in the sheets of glass and displays the defects as a defect map on a computer monitor.
In a preferred embodiment, there are at least two first lasers and at least two second lasers, preferably with at least two cylindrical lens systems wherein each of the first lasers is located at the focal point of a respective cylindrical lens system and each of the second lasers is located at a distance from a respective cylindrical lens system that is greater than that of the first lasers, each second laser being located off of the axis of the respective cylindrical lens system, the first and second lasers being positioned such that light from both of the first lasers is detected by the first light detection system and light from both of the second lasers is detected by the second light detection system.
Another aspect of the present invention provides an inspection system for a sheet of glass, comprising:
a) a source of light to provide bright field illumination and means to detect said bright field illumination and variations therein; and
b) a source of light to provide dark field illumination and means to detect the dark field illumination and variations therein.
A further aspect of the present invention provides a method for inspection of a sheet of glass, comprising:
a) providing bright field illumination of a sheet of glass and detecting said bright field illumination thus obtained;
b) providing dark illumination of a sheet of glass and detecting said dark field illumination thus obtained; and
c) analyzing said bright field and dark field illumination for presence of defects in said sheet of glass.
In a preferred embodiment of the method of the invention, the illumination is analyzed using computer software.
In another embodiment, the inspection system is tuned to detect defects having a size of greater than 100 microns, but not recognize smaller defects e.g. dust.
An additional aspect of the invention provides a method for inspection of a sheet of glass for defects therein, in apparatus comprising:
a) a first laser and a second laser, each of the first laser and second laser providing a sheet of light;
b) a cylindrical lens system, said lens system having a focal point on the main optical axis thereof;
c) a first light detection system and a second light detection system;
passing light from the first laser located at the focal point of the lens system and from the second laser located at a distance from the lens system that is greater than that of the first laser through said lens system, said second laser being located off of the axis of the lens system, the light from the first laser being collimated light,
passing said light through a sheet of glass to be inspected; and
detecting light from the first laser with the first light detection system and variations therein; and
detecting light from the second laser with the second light detection system and variations therein.